1. Field of the Invention
This invention relates to planar terminated surface mounted capacitors and more particularly to a capacitor which is hermetically sealed in a ceramic case.
2. Description of the Background Art
Direct mounting of electrical components, such as wound metallized polyester or metallized polycarbonate capacitors, is useful in thin and thick integrated hybrid circuitry. In previous attempts to accomplish this, unencapsulated capacitors were often used. Such capacitors required careful handling, and their protruding terminal leads were not strong. In fact, even after they were connected, they could not withstand most military environmental requirements.
Further, since many present day applications required components that could be planar mounted, encapsulated finished components having terminal leads could not be utilized.
Also, since such planar connections were usually accomplished by reflow soldering or similar means, it became apparent that what was needed was a component having the strength and versatility and heat resistance of an encapsulated element with the advantages of planar external terminal connections.
An ideal capacitor for this type of arrangement is a small chip capacitor of the type described in U.S. Pat. No. 4,378,620 which is incorporated herein by reference. This capacitor, however, was formed by bonding a lead to the electrodes in each edge thereby preventing planar mounting. Converting these finished electrical components to elements having planar terminations has been described in applicant's U.S. patent application Ser. No. 348,401, now U.S. Pat. No. 4,455,591 issued June 19, 1984. In this method, the leads were cut and end caps were placed over the ends of the component.
Applicant's U.S. patent application Ser. No. 586,014 teaches fabricating planar terminated capacitors which do not require cutting leads before placement of the end caps. However, these capacitors need an epoxy sleeve having low thermal resistance and were not hermetically sealed.
Furthermore, the difference in thermal coefficients between capacitor case (with higher heat resistance) and the capacitor element may be of large magnitude. This may result in loosening of the caps and lowered reliability especially in applications with wide temperature excursions.
It is, therefore, an object of the present invention to provide hermetically sealed planar terminated capacitors which may be fabricated directly from the capacitor elements having high thermal resistance.
It is a further object to provide a surface mounted capacitor which maintains reliability when there are large thermal excursions. PG,5